A plumb bob, plumb bob level, or plummet, is a weight, usually with a pointed tip on the bottom, suspended from a string and used as a vertical reference line, or plumb-line. It is a precursor to the

spirit level A spirit level, bubble level, or simply a level, is an instrument designed to indicate whether a surface is horizontal (level) or vertical ( plumb). Different types of spirit levels may be used by carpenters, stonemasons, bricklayers, oth ...

and used to establish a vertical datum. It is typically made of stone, wood, or lead, but can also be made of other metals. If it is used for decoration, it may be made of bone or ivory. The instrument has been used since at least the time of ancient EgyptDenys A. Stocks.
Experiments in Egyptian archaeology: stoneworking technology in ncient Egypt
'. Routledge; 2003. . p. 180. to ensure that constructions are " plumb", or vertical. It is also used in

surveying Surveying or land surveying is the technique, profession, art, and science of determining the terrestrial two-dimensional or three-dimensional positions of points and the distances and angles between them. A land surveying professional is ...

, to establish the

nadir The nadir (, ; ar, نظير, naẓīr, counterpart) is the direction pointing directly ''below'' a particular location; that is, it is one of two vertical directions at a specified location, orthogonal to a horizontal flat surface. The direc ...

with respect to

gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the str ...

of a point in space. It is used with a variety of instruments (including levels,

theodolite A theodolite () is a precision optical instrument for measuring angles between designated visible points in the horizontal and vertical planes. The traditional use has been for land surveying, but it is also used extensively for building and ...

s, and steel tapes) to set the instrument exactly over a fixed

survey marker Survey markers, also called survey marks, survey monuments, or geodetic marks, are objects placed to mark key survey points on the Earth's surface. They are used in geodetic and land surveying. A '' benchmark'' is a type of survey marker that ...

or to transcribe positions onto the ground for placing a marker.

Etymology

The ''plumb'' in ''plumb bob'' derives from Latin '' plumbum'' ('

lead Lead is a chemical element with the Symbol (chemistry), symbol Pb (from the Latin ) and atomic number 82. It is a heavy metals, heavy metal that is density, denser than most common materials. Lead is Mohs scale of mineral hardness#Intermediate ...

'), the material once used for the weighted '' bob'' at the end. The adjective '' plumb'' developed by extension, as did the noun '' aplomb'', from the notion of "standing upright".

Use

Until the modern age, plumb bobs were used on most tall structures to provide vertical datum lines for the building measurements. A section of the scaffolding would hold a plumb line, which was centered over a datum mark on the floor. As the building proceeded upward, the plumb line would also be taken higher, still centered on the datum. Many cathedral

spire A spire is a tall, slender, pointed structure on top of a roof of a building or tower, especially at the summit of church steeples. A spire may have a square, circular, or polygonal plan, with a roughly conical or pyramidal shape. Spires are ...

domes A dome () is an architectural element similar to the hollow upper half of a sphere. There is significant overlap with the term cupola, which may also refer to a dome or a structure on top of a dome. The precise definition of a dome has been a m ...

and

tower A tower is a tall structure, taller than it is wide, often by a significant factor. Towers are distinguished from masts by their lack of guy-wires and are therefore, along with tall buildings, self-supporting structures. Towers are specifi ...

s still have brass datum marks inlaid into their floors, which signify the center of the structure above. Lot hg

A plumb bob and line alone can determine only a vertical reference. However, if they are mounted on a suitable scale the instrument may also be used as an

inclinometer An inclinometer or clinometer is an instrument used for measuring angles of slope, elevation, or depression of an object with respect to gravity's direction. It is also known as a ''tilt indicator'', ''tilt sensor'', ''tilt meter'', ''slope ...

to measure angles to the vertical. Ancient Egyptians used a plumb line attached to the top outer part of a tool resembling a letter '' E''; when placed against a wall, the plumb line would indicate a vertical line. An A-frame level with a plumb line hung from the vertex was also used to find horizontal; these were used in Europe until the mid–19th century. A variation of this tool has the plumb line hung from the top of an inverted '' T'' shape. The early

skyscraper A skyscraper is a tall continuously habitable building having multiple floors. Modern sources currently define skyscrapers as being at least or in height, though there is no universally accepted definition. Skyscrapers are very tall high-ri ...

s used heavy plumb bobs, hung on wire in their elevator shafts. A plumb bob may be in a container of water (when conditions are above freezing temperatures), molasses, very viscous oils or other liquids to dampen any swinging movement,Staley, W. W.. ''Introduction to mine surveying'',. 2nd ed. Stanford University, Calif.: Stanford University Press, 1964. Print. 138. functioning as a

shock absorber A shock absorber or damper is a mechanical or hydraulic device designed to absorb and damp shock impulses. It does this by converting the kinetic energy of the shock into another form of energy (typically heat) which is then dissipated. Mos ...

Determining center of gravity of an irregular shape

Students of

figure drawing A figure drawing is a drawing of the human form in any of its various shapes and postures using any of the drawing media. The term can also refer to the act of producing such a drawing. The degree of representation may range from highly detailed, ...

will also make use of a plumb line to find the vertical axis through the

center of gravity In physics, the center of mass of a distribution of mass in space (sometimes referred to as the balance point) is the unique point where the weighted relative position of the distributed mass sums to zero. This is the point to which a force may ...

of their subject and lay it down on paper as a point of reference. The device used may be purpose-made plumb lines, or simply makeshift devices made from a piece of string and a weighted object, such as a metal washer. This plumb line is important for lining up anatomical geometries and visualizing the subject's center of balance.

References

External links

60 oz. Plumb Bob

{{DEFAULTSORT:Plumb Bob Inclinometers Measuring instruments Surveying instruments Woodworking measuring instruments Orientation (geometry) Carpentry tools Stonemasonry tools

Etymology

Use

Determining center of gravity of an irregular shape

See also

References

External links